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An Experimental Investigation and Modeling of the Flow Rate of Refrigerant 22 Through the Short Tube Restrictor (NISTIR 89-4120)



D. A. Aaron, Piotr A. Domanski


Refrigerant 22 flow through short tube restrictors was investigated. The analysis pertained to initially subcooled refrigerant flowing through short tubes with 5 < L/D < 20. The flow conditions studied were those typically found in heat pumps. Flow dependencies upon upstream subcooling, upstream pressure, downstream pressure, tube length, tube diameter, entrance chamfering and exit chamfering were examined. A correlation and flow charts for mass flow rate prediction were developed from a large experimental data base. For a given inlet pressure and subcooling, the flow behaved differently depending upon the downstream pressure level. For downstream pressures greater than the approximate liquid saturation pressure of the entering refrigerant, the flow was strongly dependent upon the downstream pressure, as is found for single-phase fluid flowing through a duct. However, for downstream pressures below the saturation pressure, as is typically found during heat pump operation, the flow demonstrated a very weak dependence upon the downstream pressure and could be termed as non-ideal choked flow. For the case when the downstream pressure was below the saturation pressure, the mass flow rate was directly proportional to upstream subcooling, upstream pressure and cross sectional area, and was inversely proportional to short tube length. The mass flow rate was highly sensitive to inlet chamfering and insensitive to exit chamfering.
NIST Interagency/Internal Report (NISTIR) - 89-4120
Report Number


air conditioner, choked flow, expansion device, heat pump, orifice, pluge orifice, restrictor, short tube restrictor


Aaron, D. and Domanski, P. (1989), An Experimental Investigation and Modeling of the Flow Rate of Refrigerant 22 Through the Short Tube Restrictor (NISTIR 89-4120), NIST Interagency/Internal Report (NISTIR), National Institute of Standards and Technology, Gaithersburg, MD, [online],, (Accessed June 19, 2024)


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Created June 30, 1989, Updated October 12, 2021